[1] Green tea originated in China in the late 1st millennium BC, and since then its production and manufacture has spread to other countries in East Asia.

Steeping too hot or too long results in the release of excessive amounts of tannins, leading to a bitter, astringent brew, regardless of initial quality.

[citation needed] Extracts are sold over the counter in liquid, powder, capsule, and tablet forms,[3][8] and may contain up to 17.4% of their total weight in caffeine,[9] though decaffeinated versions are also available.

[11] Regular green tea is 99.9% water, provides 1 kcal per 100 mL serving, is devoid of significant nutrient content (table), and contains phytochemicals such as polyphenols and caffeine.

[16][17] A 2020 review by the Cochrane Collaboration listed some potential adverse effects of green tea extract including gastrointestinal disorders, higher levels of liver enzymes, and, more rarely, insomnia, raised blood pressure, and skin reactions.

[21] Green tea interferes with the chemotherapy drug bortezomib (Velcade) and other boronic acid-based proteasome inhibitors, and should be avoided by people taking these medications.

[22] A meta-analysis of observational studies reported an increase in one cup of green tea per day was correlated with slightly lower risk of death from cardiovascular causes.

[24][25] Meta-analyses of randomized controlled trials found that green tea consumption for 3–6 months may produce small reductions (about 2–3 mm Hg each) in systolic and diastolic blood pressures.

[29][30][33] A 2013 Cochrane meta-analysis of longer-term randomized controlled trials (>3 months duration) concluded that green tea consumption lowers total and LDL cholesterol concentrations in the blood.

[36][37][38] In 2018, a scientific panel for the European Food Safety Authority reviewed the safety of green tea consumption over a low-moderate range of daily EGCG intake from 90 to 300 mg per day, and with exposure from high green tea consumption estimated to supply up to 866 mg EGCG per day.

As a result of these methods, maximum amounts of polyphenols and volatile organic compounds are retained, affecting aroma and taste.

The green tea plants are grown in rows that are pruned to produce shoots in a regular manner, and in general are harvested three times per year.

[42] On 17 June 2011, at Charles de Gaulle airport in Paris, France, radioactive caesium of 1,038 becquerels per kilogram was measured in tea leaves imported from Shizuoka Prefecture, Japan as a result of the Fukushima Daiichi nuclear disaster on 11 March, which was more than twice the restricted amount in the European Union of 500 becquerels per kilogram.

[44] Japanese Minister for Consumer Affairs and Food Safety Renhō stated on 3 June 2011 that "there are cases in which aracha [whole leaves of Japanese green tea] are sold as furikake [condiments sprinkled on rice] and so on and they are eaten as they are, therefore we think that it is important to inspect tea leaves including aracha from the viewpoint of consumers' safety.

"[45] In 2018, the US Food and Drug Administration updated its import status on Japanese products deemed to be contaminated by radionuclides, indicating that tea from the Ibaraki prefecture had been removed from the list by the Government of Japan in 2015.

[47][48] While Chinese green tea was originally steamed, as it still is in Japan, after the early Ming dynasty it has typically been processed by being pan-fired in a dry wok.

The Zen Buddhist priest Eisai (1141–1215), founder of the Rinzai school of Buddhism, brought tea seeds from China to plant in various places in Japan.

[61] The largest tea-producing area today is Shizuoka Prefecture, which accounts for 40% of total Japanese sencha production.

[62][61] Other major tea-producing regions include the island of Kyushu and the prefectures of Shiga, Gifu, and Saitama in central Honshu.

Japanese tea production is heavily mechanized, and is characterized by the use of modern technology and processes to improve yields and reduce labour.

Because of the high cost of labour in Japan, only the highest quality teas are plucked and processed by hand in the traditional fashion.

[65] Most Japanese teas are blended from leaves grown in different regions, with less emphasis on terroir than in the Chinese market.

[67] Popular Japanese green teas include: According to Record of Gaya cited in Memorabilia of the Three Kingdoms, the legendary queen Heo Hwang-ok, a princess of the Ayodhya married to King Suro of Gaya, brought the tea plant from India and planted it in Baegwolsan, a mountain in current Changwon.

[101] Vietnamese tea culture is ancient, but large scale cultivation was introduced in the late 19th century by French colonists who ran the first plantations in the Phú Thọ area.